In a large pot, heat the oil over medium-high heat and brown the roast for 8 minutes, turning to brown on all sides.

Sprinkle the onion powder, garlic powder, oregano, salt, and pepper over the roast, then add the onions and tomatoes to the pot.

Reduce the heat to low, cover, and simmer for 2-1/2 to 3 hours, or until the roast is tender.

Slice the roast across the grain and serve with the pan juices.